1. Field of the Invention
This invention relates to the field of hydrocarbon conversion with fluid catalytic cracking catalyst. In particular, it relates to the regeneration of coked catalyst by conversion of coke on catalyst with control of the temperature of regeneration.
2. Description of the Prior Art
The FCC process converts petroleum feedstocks boiling in the gas oil boiling range to lighter products such as gasoline. To obtain maximum conversion efficiency from the very active zeolite cracking catalyst, it is necessary to remove as much coke as possible during the regeneration step of the FCC process. Accordingly, modern regenerators are operated in the high temperature regeneration mode. Regeneration temperatures in the range of to 538.degree. C. to 787.degree. C. (1000.degree. F. to 1450.degree. F.), more preferably 621.degree. C. to 732.degree. C. (1150.degree. F. to 1350.degree. F.) and most preferably 677.degree. C. (1250.degree. F.) to 732.degree. C. (1350.degree. F.) are employed.
Increasingly, catalytic cracking units are being adapted to the conversion of feedstocks heavier than gas oil. Such carbo-metallic hydrocarbon oils contain relatively large amounts of coke precursors, e.g. asphaltenes and heavy aromatic hydrocarbons. In addition, carbo-metallic cracking feedstocks contain complex organo-metallic compounds which deposit on the cracking catalyst as it circulates between the cracking zone and the regeneration zone. The most difficult problem encountered in the conversion of carbo-metallic oils is the high temperatures which can occur during the burning of carbon from the fluid catalyst particles. Since the hi-tech zeolite cracking catalyst by prolonged exposure to temperatures above about 704.degree. C. (1300.degree. F.) to 815.degree. C. (1500.degree. F.) is known to deteriorate, it is essential that the regeneration procedure be carefully controlled.
Various types of catalyst coolers are presently applied to regenerators and most of these coolers are based on indirect heat exchange employing tubular heat exchangers located inside or outside of the regenerator. Prior art FCC regenerators with coolers are disclosed in U.S. Pat. Nos. 2,377,935; 2,386,491; 2,662,050; 2,492,948; and 4,374,750.
The regenerator of the present invention is particularly applicable to control of catalyst cooling in situations where the catalytic cracking unit is revamped to convert feedstocks heavier than gas oil on a full or part-time basis. Two such cracking units are shown in Hydrocarbon Processing September, 1962, page 156 and Hydrocarbon Processing, September, 1970, page 177.
In addition, the process and apparatus of the present invention can be used in the regeneration of coked non-catalytic fluid solids like those used for decarbonization and demetallization of carbo-metallic feedstocks. One such process is disclosed in U.S. Pat. Nos. 4,469,588 to Hettinger et al (Ashland Oil, Inc.) 4,434,044 to Busch et al (Ashland Oil, Inc.) and 4,414,098 to Zandona et al (Ashland Oil, Inc.)